The present invention relates to determining a tag to noise ratio (TNR) for radio frequency identification (RFID) tags.
Shipping packages typically involves moving the packages to different locations in a shipping warehouse in preparation for the packages being loaded onto trucks. Shipping warehouses can use RFID systems to track inventory. RFID tags, which can be passive or active, are disposed on the inventory (e.g., individual packages or pallets) in the warehouse and are programmed with information identifying the associated inventory. The identifying information is read from the RFID tags by RFID readers. In one example, the RFID readers are located at loading docks or along conveyor belts so that the RFID system can detect when RFID tags (and the corresponding inventory) pass through.
However, in noisy or dense RFID environments (e.g., environments with large populations of RFID tags or a high density of RFID readers), a package can be detected by multiple RFID readers which are assigned to different locations in the warehouse. For example, during a first time instance, an RFID tagged package located in a loading zone for a first dock door may be detected by the RFID reader at that location. However, as the environment changes, during a second time instance the RFID tagged package may be detected by a RFID reader at a neighboring dock door. In response, an inventory tracking system may mistakenly determine the package has been moved to a different dock door (e.g., a false positive) and dispatch an associate to move the package back to the loading zone for the first dock door when in fact the package is stationary and has not changed dock door locations. As such, these false positives can generate false troubleshooting events which unnecessarily add to the workload of the associates in the warehouse.
The inventory tracking system can compare different metrics to identify the location of the tagged package when detected by multiple readers. For example, the tracking system can compare the instantaneous or average signal strength of signals received from the tag at the readers. In other examples, the system may compare the peak signal strength or the number of times the tag was detected by the readers. However, in a dense and noisy RFID environment, these factors may be insufficient to accurately determine the location of tagged packages.